commit 8ac85f257f15dbde3918875f696dde3bca8afa4d
author David 'Digit' Turner <digit@google.com> Fri Oct 21 15:27:59 2016 +0200
committer David 'Digit' Turner <digit@google.com> Thu Oct 27 18:22:32 2016 +0200
tree 38b2e5111f14c1999b5a631f893a205868fb6feb
parent 502d49aa9c9b377deccc41002965188717f95c67

hax: Add HAX_DISABLE_UNRESTRICTED_GUEST env. variable.

After this patch is applied, if HAX_DISABLE_UNRESTRICTED_GUEST
is defined to either '1' or 'true' in the environment, the VT-x
"unrestricted guest" CPU feature will be ignored.

This will force the emulator to use HAX emulation inside a
single TCG vCPU thread (while unrestricted guest mode allows
one to run multiple vCPUs on multiple cores, and uses a different
CPU emulation code path).

This is useful to debug the code path used when running the
emulator on pre-2010 CPUs, which don't support unrestricted
guest mode.

Change-Id: Ice4840ecec8ac6c5f4be155e7e600f3d907a374a

target-i386/hax-all.c

diff --git a/target-i386/hax-all.c b/target-i386/hax-all.c
index 197e817..92401be 100644
--- a/target-i386/hax-all.c
+++ b/target-i386/hax-all.c
@@ -213,8 +213,22 @@
         return -ENXIO;
     }
 
-    if ((cap->winfo & HAX_CAP_UG))
+    if ((cap->winfo & HAX_CAP_UG)) {
         ug_support = 1;
+    }
+
+    // NOTE: If HAX_DISABLE_UNRESTRICTED_GUEST is defined and set to 1 or 'true'
+    // then disable "unrestricted guest" on modern cpus that support it. This
+    // is useful to test and debug the code-path used for older CPUs that
+    // don't have that feature.
+    if (ug_support) {
+        const char* env = getenv("HAX_DISABLE_UNRESTRICTED_GUEST");
+        if (env && (!strcmp(env, "1") || !strcmp(env, "true"))) {
+            DPRINTF(
+                "VTX unrestricted guest disabled by environment variable.\n");
+            ug_support = 0;
+        }
+    }
 
     if (cap->wstatus & HAX_CAP_MEMQUOTA) {
         if (cap->mem_quota < hax->mem_quota) {